There are many methods to determine vacancy and the HUD regulations specifically state these four in Attachment 2, paragraph I, sub-paragraph C:
(i) checking utility meters to determine if they are on
(ii) contacting the listing broker if there is a for sale or rent sign on the property
(iii) observing general maintenance and
(iv) speaking to neighbors.
Other methods may include surveillance, phone, cable, internet providers, mail delivery personnel, etc.